There are several different techniques known to treat unclean water containing different pollutions. Depending on the type of pollutant, one or more techniques may be used either alone or in combination. When treating unclean water comprising particles suspended in the water, e.g. in a sewage system, the system may comprises different mechanical filter types, one or more biological processing steps and one or more chemical processing steps.
In a sewage system, contaminants are removed from wastewater and household sewage, both effluents and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants. The main purpose is to produce an environmentally-safe fluid waste stream with more or less clean water that can be discharged in nature, e.g. in a river, see or lake, and a solid waste in the form of sludge that can be disposed of or reused.
The waste water of the sewage system may be more or less clean. When undesirable chemicals, materials, and biological contaminants have been removed from contaminated water, the water is defined as purified and can be used for a specific purpose, e.g. as drinking water or other purposes, including meeting the requirements of medical, pharmacology, chemical and industrial applications. In general the methods used to purify water includes physical processes such as filtration and sedimentation, biological processes such as slow sand filters or active sludge and chemical processes such as flocculation and chlorination.
Flocculation is a process which clarifies the water by removing any turbidity, i.e. suspended particles or colloid, or colour so that the water is clear and colourless. Flocculation removes the suspended particles by causing a precipitate to form in the water. By stirring the water, the particles will stick together to form bigger particles by adsorbing onto the surface of small precipitate particles which then grows into larger particles as a coagulation product which can easily be removed. In the flocculation process, a coagulant or flocculation agent may be used to aid the flocculation process. Such coagulants comprise iron, aluminum or synthetic polymers.
Traditional flocculation processes are known under such names as Pulsator, Super Pulsator, Cyclofloc, Cirkulator, Fluorapid and Accelator. All these flocculation processes need different mechanical parts and are designed as large nonflexible structures. They further require a high maintenance to function properly.
U.S. 20070114184 discloses a method and apparatus for treating wastewater. The apparatus comprises a reactor having a centrally arranged flow channel. An agitator in the form of a propeller is disposed within the flow channel which creates a downward flow of water or wastewater through the flow channel. A reagent is injected into the water or wastewater and the agitator within the flow channel serves to mix the reagent with the water or wastewater passing there through.
U.S. 20040011745 discloses a combined degassing and flotation tank for separation of a water influent containing considerable amounts of oil and gas. A rotational flow is created in the tank which forces the lighter components such as oil and gas droplets towards an inner concentric cylindrical wall where they coalesce and rise to the surface of the liquid whereas the heavy particles sink to the lower part where they may be removed as sludge. The water is discharged via an outlet in the lower part of the tank. The combined degassing and flotation tank is particular suited for use in oil production at sea for removal of oil.
U.S. 20050115881 discloses a water purification installation having a coagulation area, a flocculation area, an area for mixing the flocculated water with pressurized water delivered by micro bubbles, and a flotation area. Suspended matter, which is brought to the surface by the micro bubbles, is evacuated from the upper part of the flotation area. The lower part of the flotation area includes means of collecting the clarified water.
WO 05063630 A discloses a method for treating waste water, e.g. municipal waste water including sewage, which comprises adding a particulate material to the waste water, and then performing a flotation process so that the particulate material rises to the surface of the waste water, entraining solids material in the waste water. The particles may comprise bubbles of soda lime borosilicate glass.
CN 1312226 A discloses a method and arrangement for counter flow water treatment, where micro bubbles flow counter to downward flowing raw water, where flocculate can contact with upward flowing bubbles such that the bubbles may cohere with flocculate to produce a suspension sludge layer, which can provide contact flocculation and sludge filtration action on raw water.
CN 1397503 A discloses a process for cleaning water including mixing the flocculants with the water to be treated in a water inlet pump, where the reaction between air bubbles and flocculants is obtained in a counter current flow, where the resultant water is discharged from the bottom of the reactor, and the waste is discharged from the top of the reactor.
DE 3031755 A1 discloses a water cleaning process using an inner chamber in which the water is circulated and where floatation takes place. Chemicals are used to flocculate the particles in the water.
JP 11300381 A discloses a water cleaning process in which flocculation and decanting is used to treat the water.
These and similar known processes and systems may work well in specific cases. There is however still room for improvements.